#include <fstream>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

int cnt, n, v[2000005], i, j;

int main()
{
    fin >> n;
    for (i = 2; i <= n; i++)
        v[i] = 1;
    for (i = 2; i <= n; i++)
        if (v[i] == 1){
            cnt++;
            for (j = i + i; j <= n; j += i)
                v[j] = 0;
    }
    fout << cnt;
    return 0;
}